Solutions of 3D Reflection Equation from Quantum Cluster Algebra Associated with Symmetric Butterfly Quiver
Rei Inoue, Atsuo Kuniba
TL;DR
This work constructs a novel pair of operators $(R,K)$ that solve the three-dimensional reflection equation by embedding the problem in a quantum cluster-algebra framework based on Symmetric Butterfly quivers of type $C$. The $R$-operator matches the previously known construction built from four quantum dilogarithms, while the new $K$-operator involves ten dilogarithms, with both decomposed into a dilogarithm part and a monomial part that can be moved by adjoint actions. The core technical achievement is a full 3DRE verification: under carefully chosen parameter constraints, the $R$- and $K$-operators satisfy the boundary analogue of the tetrahedron equation, with a 46-term dilogarithm identity and a well-defined algebraic structure in both quantum-$Y$ and $q$-Weyl representations. The paper also shows how the SB-construction reduces to the FG quiver setting, linking the new boundary solution to established 2D boundary integrable structures and suggesting routes to broader applications and matrix-element calculations. Overall, the work deepens the connection between quantum cluster algebras, dilogarithm identities, and higher-dimensional integrable boundary systems, offering a robust framework for future boundary solvable models.
Abstract
We construct a new solution $(R,K)$ to the three-dimensional reflection equation, a boundary analogue of the tetrahedron equation. The $R$-operator is the one obtained by Sun, Terashima, Yagi, and the authors in 2024, involving four quantum dilogarithms with arguments in the $q$-Weyl algebra. The new $K$-operator similarly involves ten such quantum dilogarithms. Our approach is based on the quantum cluster algebra associated with the symmetric butterfly quiver on the wiring diagram of type C.
